linux-yocto-dev: allow static SRCREVs via include

linux-yocto-dev: allow static SRCREVs via include

The linux-yocto dev recipe is intended to track the latest revisions of the
kernel tree by default. To control revision churn, and integrate into a
regular build schedule having the ability to specify a set of SRCREVs without
modifying the recipe itself is desired.

So we introduce an optional include file, and variables that control whether
or not the static SRCREVs are used: USE_MACHINE_AUTOREV and USE_META_AUTOREV,
to add this flexibility.

(From OE-Core rev: 5877781d1dcb2883d00097b66ff2481a4a5ff930)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>